Precise Delivery of Physiological Doses of Melatonin in Planta to Control Postharvest Physiology and Extend Shelf Life Outside the Cold Chain

Postharvest management of leafy vegetables requires refrigeration to control their rapid deterioration and loss, which accounts for ∼30% of total food waste. Here, silk microneedles with a length of 700 μm were used to deliver physiological doses of melatonin (approximately 22 μg) in the leafy vegetable Pak choy (Brassica rapa subsp. chinensis) and successfully extended the shelf life of the harvested crop by 4 and 10 days at room temperature (25 °C) and under refrigeration (4 °C), respectively, compared to nontreated control plants. The exogenous dose of melatonin did not alter the natural concentration of the hormone in the harvested plants. Transcriptome analysis showed that melatonin regulates senescence by modulating auxin synthesis, the antioxidant system, and chlorophyll degradation. Overall, silk microneedles can be used to precisely deliver in harvested products compounds that extend their shelf life outside the cold chain.